What is the main message in "The Veldt"?

As in so much of his fiction, Bradbury warns us against allowing technology to get the upper hand in our lives.
In this story, the Hadley parents initially believe they are doing the best possible thing in buying the state-of-the-art HappyLife home, an expensive nursery with televised walls which does everything for them.
What they do not realize until too late is that a technology that does everything for a family will soon come to control the family. Lydia feels anxious and displaced with nothing to do. The children, Wendy and Peter, soon come to see the nursery as a better and more indulgent parent to them than their own parents. They come to hate their real parents as an impediment to their happiness.
As the story illustrates, the old-fashioned virtues of a simple home and parents who actually raise and discipline their children are far healthier than relying on technology to make life easier. In the end, in fact, technology does not make life easier but instead leads to death.

One could argue that Bradbury's main message in the short story "The Veldt" is that over-reliance on technology can negatively affect humanity. In the short story, the completely automated HappyLife Home does everything for the Hadley family, and the children have virtually no responsibilities. George and Lydia rely on their automated smart home to complete every task, and their children realize that the parents are irrelevant. Wendy and Peter become consumed with their nursery, which displays three-dimensional realistic landscapes that reflect their thoughts and feelings. Wendy and Peter view their technologically advanced nursery as more important than their parents, and their negative feelings toward George and Lydia are reflected on the nursery screens as the African veldt. When the psychologist David McClean visits the Hadley home, he encourages George and Lydia to close the nursery for a while and says,

You’ve let this room and this house replace you and your wife in your children’s affections. This room is their mother and father, far more important in their lives than their real parents.

After their parents lock the nursery, Wendy and Peter throw tantrums and become increasingly hostile toward them. Eventually, George and Lydia find themselves locked in the nursery, which displays the African veldt that comes to life and leads to their death. Overall, Bradbury's short story explores the negative effects of over-reliance on technology by illustrating how technology can destroy a family and ruin the most meaningful relationships between parents and their children.

Arguably, the main message of "The Veldt" is that people should not be over-reliant on technology, and this is shown clearly by the story's main events.
When the Hadleys install the HappyLife Home, they believe that they are doing something good for their children. As George says:

But nothing’s too good for our children.

However, as the story progresses, we see that the HappyLife Home has a number of negative aspects. For a start, Lydia feels that the HappyLife Home threatens her role as a mother since she is no longer required to carry out her maternal tasks, like feeding and clothing her children. The new nursery takes care of everything, leaving her feeling without purpose.
In addition, the story's violent conclusion, in which the Hadleys are attacked by lions, demonstrates that the HappyLife Home is indeed the stuff of nightmares.
Through these events, Bradbury warns his readers that while technology may appear to offer a solution to every problem, we must proceed with extreme caution before accepting it into our lives.